With spark-ignition engines it is necessary particularly when linear lambda controlling is used to perform forced excitation for insuring optimal exhaust-gas conversion and for diagnostic purposes, with a rich combustion-air ratio and a lean combustion-air ratio being set alternately within the scope of forced exciting.
However, changing the combustion-air ratio within the scope of forced exciting results in a corresponding change in engine-drive torque, which in the case of internal-combustion engines having two cylinder lines is compensated through having forced exciting and hence also changing of the two cylinder lines' engine-drive torque take place in phase opposition.
It is furthermore known that in the case of internal-combustion engines having two cylinder lines the engine is controlled by means of a master-slave system, with a superordinate master control device controlling one cylinder line and a subordinate slave control device controlling the other cylinder line. Dividing engine controlling in that way between a master control device and a slave control device offers the possibility of individually calculating the parameters for forcibly exciting the two cylinder lines. Thus the master control device can calculate thresholds for the oxygen charge of the first combustion-chamber group's catalytic exhaust-gas converter while the slave control device calculates thresholds for the oxygen charge of the second cylinder line's catalytic exhaust-gas converter. The lambda deviation for the two cylinder lines' forced excitation can, moreover, also be calculated separately in the master control device and slave control device.
In the case of engine controlling of said kind by means of a master control device and a slave control device there is, however, as yet no known solution for enabling the individual cylinder lines to be forcibly excited in a mutually opposing manner for compensating variations in engine-drive torque during forced excitation.